Hydrocarbon conversion processes often employ multiple reaction zones through which hydrocarbons pass in series flow. Each reaction zone in the series often has a unique set of design requirements. Generally, one such design requirement of each reaction zone in the series is a hydraulic capacity, which can be the maximum throughput of hydrocarbons through that zone. An additional design requirement of each reaction zone is the capability to perform a specified degree of hydrocarbon conversion. Designing a reaction zone for a specified degree of hydrocarbon conversion, however, often results in a reaction zone that can be designed larger than the minimum size required for hydraulic capacity alone. Consequently, in hydrocarbon conversion processes having multiple reaction zones with a series flow of hydrocarbons, one reaction zone may have more hydraulic capacity than some other reaction zones in the series. As an example, in a hydrocarbon reforming process, the penultimate and/or last reforming reaction zone often has excess hydraulic capacity in comparison with the first and/or second reforming reaction zone.
One solution to these shortcomings is providing staggered-bypass reactors to eliminate hydraulic capacity constraints, as a result of, e.g., catalyst pinning, from one or more reactors in a process, such as a catalytic reforming process. Generally, in catalytic reforming the catalyst circulates from a series of reaction zones to a regenerator and then returns to the first zone. Additional advantages of staggered-bypass reactors can include eliminating bottlenecks in other equipment, such as fired heaters or recycle gas compressors.
However, a shortcoming of staggered-bypass reactors is that the overall catalyst utilization is somewhat reduced because not all the hydrocarbons pass through all the reactors. To obtain the same conversion with a reactor section using staggered-bypass reactors, generally the reactor inlet temperatures are increased somewhat higher than the reactor inlet temperatures required without the bypassing. In units using larger bypassing flow rates, such as greater than about 15%, the resultant temperature increase may limit the increased feed rate or increased reformate octane potential of the unit because the existing equipment is limited with respect to the temperatures or pressures created by the higher temperatures. Desirably, it would be beneficial to overcome this limitation in a unit having staggered-bypass reactors. Although staggered-bypass reactors can eliminate the problems associated with hydraulic capacity restraints, increasing the feed rates through the reactors without having to increase the temperature would be desired.